Chronic administration of SCH 23390 enhances spontaneous searching and locomotor activity of rats. An open field...

The influence of dopamine D1 receptor supersensitivity, induced by repeated SCH 23390 administration, on rat spontaneous behavior was studied in an open field test. The frequency of line crossing, rearing and looking-into-holes episodes was evaluated as a part of the locomotor and exploratory behavior. SCH 23390 was injected subcutaneously in a dose of 0.5 mg/kg, one injection per day for 21 days. Controls were injected with isotonic saline. When the open field test was applied one day after the last treatment, all the tested parameters were significantly enhanced in rats treated repeatedly with SCH 23390. The effects were diminished after 3 days and had almost disappeared after 7 days. It is argued that supersensitivity of dopamine D1 receptors is responsible for the increase in locomotion and exploration.